Continuously variable transmissions (CVT) for engines may allow a seamless variation in gear ratio of an employed gear train. However, conventional CVT's use steel belts or friction couplings between rotating components of the gear train such that the gear ratios may be varied. These friction couplings or belts may be unable to work under heavy loads or be implemented in heavy duty applications. Moreover, such friction couplings when constructed to adapt to heavy duty applications may be bulky and of less reliability.
U.S. Pat. No. 7,588,509 relates to two parallel planetary gear sets with a common sun gear output geared to a hydraulic pump and motor system. Input is applied to both planetary gear sets in parallel. Output is from both planetary gear sets in parallel. Two planetary gear set members, one in each set, are geared to the pump and motor and are used to control the ratio of the infinitely variable gear transmission (IVGT). The displacement ratio of the pump and motor, connected to these two members, controls the ratio of the IVGT.